(1) Field of the Invention
This invention pertains to optical time domain reflectometers and to the use of such devices in determining the location of damaged portions of fiber optic cables. More particularly, this invention pertains to an inexpensive and simple configuration of an optical time domain reflectometer and the use of such a device as an integral component of a fiber optic system.
(2) Background
It is well known in the field of fiber optics that a damaged portion of a fiber optic cable will reflect at least a portion of the light traveling along the cable, back along the cable in a direction opposite the direction from which such light came. Using this phenomenon, optical time domain reflectometers (OTDR(s)) are able to locate damaged portions of fiber optic cables, at least to within a given range distance relative to known points along such cables. OTDRs typically operate by sending a very short-duration, high-power laser pulse along the optical cable, and by thereafter observing the returned reflections from the pulse. Although portions of the pulse are also reflected back by such things as connectors that are used to join individual sections of a fiber optic cable, by comparing the observed time domain reflection response to the time domain response that would be expected had the cable not been damaged, the portion of the pulse reflected by the damaged portion of the cable can be ascertained. The time delay between the emission of the laser pulse and the detection of its partial reflection back from the damaged portion of the cable can then be utilized to determine how far such light traveled, and hence the distance to the damaged portion.
Although OTDRs have been proven to be very useful, such devices are generally quite expensive due to the fact that they require components that can produce relatively high-power, short-duration laser pulses, and require multiple components that can sample relatively low-amplitude reflections during relatively small time domains with considerable precision. Additionally, such devices typically consume an appreciable amount of power.